Two pressure cooker devices loaded up with deadly shrapnel designed to maim anyone standing by and jim avila has more. It's not hard to find out how to build one. Reporter: It's not. Investigators are learning more about the anatomy of the bombs and abc news confirming the common cooking appliance used in their construction was a midsize fager brand pressure cooker. Unfortunately, the pot maker sells 50,000 a year of those in the united states. This is what remains of what investigators believe could be the crude but effective bomb used in boston. The american military knows them well. The pressure cooker bomb. Homemade and designed to maim and kill. This video of military u detonating one in afghanistan posted on youtube. This one found on the internet from the streets of nepal. So common the department of defense handbook on spotting roadside bombs warns soldiers and marines to be on the lookout for that innocent pressure cooker and publications all over the internet teach the construction of a bomb made from mom's kitchen, why so popular? Because pressure cookers seal so tightly and can be filled with nails and ball bearings and other ectiles, plus when the explosive goes off this will shatter and the metal becomes a projectile itself. The pressure cooker most likely was some type of container that would add more fragmentation. Reporter: Walt houston STUDIES IEDs AND SAYS WHAT HE IS Seeing on the videos from boston indicates this pressure cooker bomb is basic, even crude with its black gunpowder explosive that leaves the telltale ied white smoke but the bomber, he says, may be more sophisticated than the bomb itself. Even using a circuit board to tell the bomb when to explode. That is a classic ied design. Reporter: So what was this bomber trying to do with this type of bomb? If he wanted to make a point and blast and disrupt the marathon, he didn't have to add the shrapnel. Reporter: Among the items recovered at the scene abc news has learned were a nylon black backpack, shrapnel that included ball bearings and nails and that circuit board, all items that are difficult to trace and long used in these kind of weapons.

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